The present invention is directed to a vehicular rearview mirror system and, in particular, a vehicular rearview mirror system in which an electro-optic reflective element assumes a partial reflectance level in response to a drive signal.
It is known for a mirror control to be responsive to an output of a vehicle control. For example, it is known to cause the reflectance level of an electro-optic reflective element to be forced into a high reflectance level when the vehicle is placed in reverse gear. An example of such a system is disclosed in commonly assigned U.S. Pat. No. 5,715,093 issued to Schierbeek et al., the disclosure of which is hereby incorporated herein by reference. The circuit that established the reflectance level of the reflective element monitors a switch or circuit that is actuated by the vehicle gearshift and which provides an indication that the gearshift is placed in reverse gear. In some vehicles, the reverse-gear indication has a protocol in which the indication changes from a low voltage level to a high voltage level when the vehicle is placed in reverse gear. In other vehicles, the protocol is that the reverse-gear indication changes from a high level to a low voltage level when the vehicle is placed in reverse gear. It is desirable to be able to install the same vehicle rearview mirror system in various vehicles irrespective of the protocol of the reverse-gear indication signal. The protocol, also known as a handshake, is the relationship between the reverse-gear indication signals when the vehicle is in reverse gear verses when it is not in reverse gear.